As VLSI and other integrated circuit packages and devices have become smaller, with shorter circuit traces and increased internal signal speeds, greater power density has resulted, causing increased heating of the devices and a need for improved heat sinking and better thermal management. Three methods are commonly employed for providing such thermal management. These methods are natural convection, which relies on air flow for cooling without any external forces applied to the air; forced convection where fans or blowers move air in a direction parallel to the surface of the element from which heat is being removed; and impingement cooling where the air is blown at the element to be cooled in a direction perpendicular to its surface.
Typically, heat sinks are provided with each of the three methods to improve the removal of heat from the element. While cooling fins or vanes have been employed for this purpose, cooling pins are preferably utilized with small elements, such as integrated circuits, because of their superior performance for a given volume.
Numerous pin-type heat sinks are currently on the market including many designed for use with integrated circuits. However, there are various problems unique to integrated circuits which are not fully addressed by existing devices. First, the heat generated by an integrated circuit is greatest at the center of the device and decreases toward the outer periphery. However, since the rate of heat dissipation by a heat sink is a function of the temperature gradient between the heat sink and the surrounding air, heat transfer from the heat sink can be improve if all the pins of the heat sink are at a relatively higher temperature rather than just a few pins near the center. It is therefore desirable to design the heat sink so as to reduce the temperature gradient between the center pins and those pins closer to the outer periphery.
Another desirable feature is that a single heat sink be available for use for all three methods of cooling, and that such heat sink be omnidirectional. This, for example, permits the heat sinks to be applied by the integrated circuit manufacturer or by the OEM manufacturer without regard to how the circuits will be oriented or cooled.
Another problem with integrated circuits is that the ceramic of the casing for the integrated circuit package and the metal typically employed for heat sinks have different thermal expansion and contraction characteristics. If there is a substantial area of contact between the two, and this area is fairly rigid, this difference can result in the cracking of the casing and thus in the destruction of the integrated circuit. It is therefore desirable to minimize the area of contact between the heat sink and the circuit package while still providing sufficient contact area for effective heat transfer. Finally, in order to assure uniform heat transfer between the circuit package and the heat sink, it is desirable that there be a controlled adhesive bond line between the members.
A need therefore exists for a heat sink for use with VLSI and other integrated circuit packages, or other similar elements which is designed to reduce the temperature gradient between the center and outer pins of the heat sink, which is adapted for use with all three methods of cooling, which minimizes adhesive bonding surface contact between the heat sink and the VLSI package while still providing effective heat transfer, and which is adapted for providing a controlled adhesive bond line between the heat sink and the element to be cooled.